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Mazda Lurches Forward

Q. Suddenly our car lurches when starting out in first gear. It is a 1992 Mazda Protégé LX with a 4-cylinder engine with about 103,000 miles. The car has a manual transmission. We recently had a full tune-up where the plugs, wires, O2 sensor, & fuel filter were changed. The car bucks when starting out in first gear but runs perfectly once it gets going. The lurching doesn't seem to be as strong in reverse. Any ideas?


A. From your letter it sounds like it started all of a sudden, not something that got worse over time. In that case I would say we have two possibilities here. A clutch disc has gone bad or a bad Throttle Position Sensor (TPS).

As far as the clutch disc goes, you can look at A Chattering Toyota for a detailed description of this possibility.

A TPS is easy enough to check, so here's how to do it. You'll need an ohmmeter for this test and maybe somebody to move the throttle for you. This is a case where an analog (needle) type meter is better than a digital meter. Locate the TPS, it will be mounted on one end of the throttle plate shaft. With the engine off, unplug the three wire connector and lay it aside.

On the TPS itself place one meter lead on the center pin and the other lead to either one of the other pins. One side should show an open (no needle movement) and the other should show a closed circuit (needle jumps). If both sides show open, the TPS is bad or out of adjustment. If it checks out we proceed with the next step. With the throttle halfway open repeat the test, this time you should have an open on both sides. If not, the TPS is no good. Again, if it checks out, we proceed to the next step.

With the throttle wide open, repeat the test, this time one side should read open and the other side should read closed. The results should be opposite of the test we did with the throttle closed. In other words if A and B showed closed at idle, B and C should read closed at wide open. at no time should there be continuity between A and C. If there is, the TPS is no good.

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Additional Information provided courtesy of AllDATA and Warranty Direct
© 2000-2008 Vincent T. Ciulla

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